The present invention relates to apparatus and methods for the thermal treatment of substrates, and includes a heating plate and a localizing temperature measuring device that is directed upon a surface of the substrate that faces away from the heating plate.
Such apparatus are used, for example, in the semiconductor industry in connection with processes for coating substrates, especially photo masks, in order to thermally treat the substrates for the curing and chemical pre-treating of the layers. During the thermal treatment, it is important for the subsequent usability of the substrates that the applied layers are treated as uniformly and homogeneously as possible. However, in this connection the problem occurs that due to an increased thermal radiation, a uniform thermal treatment in the corner regions of right-angled substrates, or the rim regions of round substrates, it is not possible to ensure a uniform treatment.
JP-A-04-239120 discloses an apparatus for the thermal treatment of substrates using a heating plate that is heated by a single heating spiral that can be differently controlled in segments thereof. The apparatus further has a localizing temperature measuring device that is directed upon the surface of the substrate that faces away from the heating plate. However, such an apparatus has the problem that it is not possible to ensure a uniform thermal treatment of the substrate. In particular, this apparatus has the problem that the individual segments of the heating spiral are frequently overloaded since the heating effect on the substrate caused by the heating spiral is sensed only with a delay by the localizing temperature measuring device. Therefore, the actually required heating temperature is constantly overshot or undershot due to the different segments of the heating spiral.
JP-A-01-050717 shows an apparatus for the thermal treatment of substrates and includes a lower heating plate, side heating plates, and temperature sensors for measuring the temperature of the heating plates. The temperatures measured by the temperature sensors are conveyed to appropriate control units in order to regulate the heating capacity of the heating plates. Such a control unit, many of which are known in the industry, does not, however, permit an adaptation of the heating device to the substrate temperature and is therefore suitable to only a limited extent for providing a homogeneous thermal treatment.
U.S. Pat. No. 5,715,361 discloses a rapid heating unit for semiconductor wafers. The wafers are heated by heating lamps and the temperature of the wafer is determined by a plurality of pyrometers on the surface of the wafer. As a function of determined temperature values on the wafer surface, the individual heating lamps are controlled. This apparatus has the same problems as occur with that of JP-A-04-239120.
It is therefore an object of the present invention to provide an improved homogeneity during a thermal treatment of substrates.
Pursuant to the present invention, the stated objective is realized for an apparatus for the thermal treatment of substrates via a heating plate by the following features: a plurality of separately controllable heating elements on that side of the heating plate remote from the substrate, at least one temperature sensor for sensing the temperature of the heating elements, at least one PID controller that is connected with the heating elements and with the at least one temperature sensor, a localizing temperature measuring device that is directed upon the surface of the substrate that faces away from the heating plate, a computing unit that is connected with the temperature measuring device and that determines the temperature distribution on the surface of the substrate, a process control unit that is connected to the computing unit and that determines desired or set values for the temperature for the individual heating elements as a function of the temperature distribution and further conveys these desired or set values to the PID controller. By means of an apparatus having the aforementioned features, an active adaptation of control parameters of a closed loop control circuit is made possible with the aid of external measurement results so that the substrates are subjected to a homogeneous thermal treatment. From the measured temperature values there results a temperature distribution over the substrate surface, from which the appropriately changed desired or set values for the temperature for the heating elements can be determined. These values are stored in the closed loop control circuit formed by the PID controller, the heating elements and the temperature sensor. As a result, it is possible to set the individual heating elements in such a way that the uniform temperature distribution is achieved within the substrate. In particular, a higher temperature can be prescribed for the heating elements in the problematic rim and edge regions.
To prevent a thermal induction disturbance between the individual heating elements, the heating elements are spaced from one another on that side of the heating plate that is remote from the substrate. In so doing, the heating elements are preferably disposed on projections of the heating plate. The shape and number of heating plates is adapted to the shape of the substrates that are to be treated, so that they advantageously extend along the outer contours of the substrates that are to be treated. To simplify control, all of the heating elements preferably have the same shape and size.
For an optimal setting of the heating elements that take part in the heating of the problematical rim portions, the position of the substrate relative to the heating plate is preferably variable.
Pursuant to one preferred specific embodiment of the present invention, each heating element is provided with a PID controller. The computing unit, the process control unit, and/or the PID controller are preferably combined in a single unit.
Pursuant to a further preferred specific embodiment of the present invention, the temperature measuring device is provided with a scanning device for the sequential scanning of that side of the substrate that faces away from the heating plate, in order to obtain in a straight-forward manner a localized measurement of the temperature of the substrate surface. In this connection, the scanning device is preferably provided with a movable mirror in order to be able to move the field of vision of the temperature measuring device over the substrate surface without the necessity of having to move the entire apparatus back and forth. The temperature measuring device is preferably an infrared (IR) camera.
In one preferred specific embodiment of the apparatus, the substrate is a photo mask.
The object of the present invention is realized with a method for the thermal treatment of substrates, according to which the substrate is heated with a heating plate, and the temperature of that surface of the substrate that faces away from the heatin plate is locally measured, by the following process steps:
heating the heating plate by means of a plurality of separately controllable heating elements, measuring the temperature of the heating elements, regulating the heating process with a PID controller, determining the temperature distribution on the substrate surface as a function of the measured temperatures, determining desired or set values for the temperature for the individual heating elements, and conveying the desired or set values for the temperature to the PID controller. With this method, the already aforementioned advantages of a homogeneous thermal treatment of the substrate are achieved by active feedback. In this connection, the individual heating elements are preferably regulated by means of individually associated PID controllers.
Pursuant to one preferred specific embodiment of the present invention, that side of the substrate that faces away from the heating plate is sequentially scanned during the temperature measurement in order to enable in a straightforward manner a localized temperature measurement. In this connection, the scanning is preferably achieved by moving a mirror.
Pursuant to a particularly preferred specific embodiment of the present invention, the temperature of that side of the substrate that faces away from the heating plate is measured with an IR camera. The inventive method is preferably utilized with photo masks.